1. Field of the Invention
The present invention relates to an illuminating optical system, and to a projector for projecting and displaying an image using the system.
2. Description of the Related Art
In a projector, illumination light emitted from an illuminating optical system is modulated by liquid crystal panels or the like according to image information (image signals), and the modulated illumination light is projected onto a screen, thereby achieving image display.
In the projector, it is preferable that the luminance distribution of an image to be projected and displayed be substantially uniform. For this reason, in the projector, a so-called optical integrator system is used, which is able to emit light with a substantially uniform intensity distribution onto a portion of a liquid crystal panel or the like on which image light is formed (illumination area).
FIG. 10 is an explanatory view showing a conventional illuminating optical system that constitutes an optical integrator system of a projector. An illuminating optical system 900 includes a light source device 20, a first lens array 940, a second lens array 950, and a superimposing lens 70. Optical elements are disposed with reference to a light source optical axis 20ax that is an optical axis of a substantially parallel light beam emitted from the light source device 20.
The light source device 20 includes a light source lamp 22, a reflector 24, and a collimator lens 30, and has the function of converting a light beam radially emitted from the light source lamp 22 into a substantially parallel light beam, and emitting the substantially parallel light beam.
The first lens array 940 has the function of dividing the substantially parallel light beam emitted from the light source device 20 into a plurality of sub light beams. FIG. 11 is a plan view of the first lens array 940 as viewed from the z direction in FIG. 10. In the illuminating optical system 900, the first lens array 940 is disposed so that the center point P1 coincides with the light source optical axis 20ax (FIG. 10) of the illuminating optical system. The first lens array 940 includes a plurality of first small lenses 942. Each of the first small lenses 942 is a plano-convex lens (FIG. 10) having the same shape, and the external shape as viewed from the z direction is set to be a substantially rectangular shape that is similar to the shape of an illumination area LA.
The second lens array 950 has the function of forming images of the first small lenses 942 of the first lens array 940 on the surface to be illuminated. The second lens array 950 is provided corresponding to the first lens array 940, and the external shape of each second small lens 952 is substantially the same as that of each first small lens 942 of the first lens array 940 shown in FIG. 11.
The superimposing lens 70 is a plano-convex lens having a spherical convex surface. The superimposing lens 70 has the function of superposing and emitting the plurality of sub light beams emitted from the first small lenses 942 of the first lens array 940 onto the surface to be illuminated. In this specification, xe2x80x9csurface to be illuminatedxe2x80x9d means a surface including the illumination area LA that is a desired area to be illuminated by the illuminating optical system 900. If the optical integrator system shown in FIG. 10 is used, a light application area having a substantially uniform light intensity distribution can be formed in the illumination area LA, even if the light intensity distribution of a substantially parallel light beam emitted from the light source device 20 is not uniform.
As is well known, the superimposing lens 70 having a spherical convex surface has spherical aberration. The aberration of the superimposing lens 70 increases with distance from the light source optical axis 20ax. That is, as shown in FIG. 10, the size of the light application area formed on the surface to be illuminated by sub, light beams emitted from the first small lenses 942 that are disposed on the outer periphery of the first lens array 940 is larger than that of the light application area formed on the surface to be illuminated by the sub light beams emitted from the first small lenses 942 that are disposed on the center of the first lens array 940. In this case, as shown in FIG. 10, the light application area of the sub light beams emitted from the first small lenses 942 on the outer periphery is defocused on the surface to be illuminated, and the sub light beams are applied onto an unnecessary area other than the illumination area LA, so that light emitted from the light source device cannot be efficiently utilized. Such problems becomes more noticeable as the size of the illuminating optical system is reduced, in other words, as the distance L between the superimposing lens 70 and the illumination area LA (that is, the focal distance f of the superimposing lens 70) is decreased.
The present invention is made to solve the above-described problems of the conventional art, and an object is to provide a technique that is able to efficiently utilize light emitted from a light source device.
In order to solve at least a part of the above-described problems, according to the present invention, there is provided an illuminating optical system including:
a light source device for emitting a substantially parallel light beam;
a first lens array having a plurality of first small lenses for dividing the light beam into a plurality of sub light beams; and
a superimposing lens for superimposing and applying the plurality of sub light beams emitted from the first lens array onto a surface to be illuminated,
wherein the size of each of the small lenses disposed on the outer periphery of the first lens array is set to be smaller than the size of each of the small lenses disposed on the center of the first lens array so that light application areas formed on the surface to be illuminated by the plurality of sub light beams emitted from the plurality of first small lenses have substantially the same size within a predetermined error range.
In the illuminating optical system of the present invention, since the size of each of the first small lenses of the first lens array is adjusted, the size of each of the light application areas formed on the surface to be illuminated by the sub light beams can be set to be substantially the same size within a predetermined error range, and consequently, light emitted from the light source device can be efficiently utilized.
In the illuminating optical system, each of the plurality of first small lenses may preferably have a similar shape as viewed from the direction of the central axis of the light beam.
This can easily set the size of each of the light application areas formed on the surface to be illuminated by the sub light beams to be substantially the same size within a predetermined error range.
In the illuminating optical system, the first lens array may be composed of two types of small lenses, relatively large first-type small lenses disposed on the center and relatively small second-type small lenses disposed on the outermost periphery.
If the first lens array is composed of two types of first small lenses in this way, a first lens array can be relatively easily obtained, that is able to set the size of each of the light application areas formed on the surface to be illuminated by the sub light beams to be substantially the same size within a predetermined error range.
In the illuminating optical system, each of the plurality of first small lenses may preferably have a substantially rectangular shape as viewed from the direction of the central axis, and the size of each of the first small lenses disposed on the outermost periphery of the first lens array may preferably be about 1% to 10% smaller per side with respect to the size of each of the first small lenses disposed on the center of the first lens array.
This makes it possible to efficiently adjust the size of each of the light application areas formed by the sub light beams.
Furthermore, the illuminating optical system may further include a second lens array having a plurality of second small lenses corresponding to the plurality of first small lenses of the first lens array, and of the plurality of second small lenses, a small lens that receives light emitted from the lenses disposed on the outer periphery of the first lens array may be a decentered lens.
If such a second lens array is used, positions of the light application areas formed by the sub light beams can be brought into coincidence with each other.
A second device of the present invention is a projector which may include:
any one of the above illuminating optical systems that is a first device of the present invention;
an electrooptical device having a light incident surface serving as a surface to be illuminated that is illuminated by the illuminating optical system and for modifying the incident light from the illuminating optical system according to image information; and
a optical projection system for projecting the modulated light beam obtained by the electrooptical device.
In the projector of the present invention, the above-described illuminating optical systems are used. Therefore, since the light utilization efficiency is high in the projector, it is possible to improve the brightness of an image to be projected and displayed.